| Abstract: | The evaluation of well logs from the Cerro Prieto geothermal field is made difficult by the wellbore conditions existing during the logging runs and by the complex minerology of the hydrothermal reservoir.In order to obtain well logs at the Cerro Prieto geothermal field, the wellbore must be cooled to at least the maximum operational temperature of available well-logging equipment, normally 120°C. Since undisturbed formation temperatures are usually in excess of 250°C at Cerro Prieto, the cooling of the wellbore creates an acute thermal gradient between the wellbore and the undisturbed formations. An understanding of the influence of this gradient on logging responses is necessary to establish confidence in well log evaluations.Similarly, since the mineralogic characteristics of the formations affect the well-log responses, quantitative mineralogic studies of wellbore cuttings and core make an important contribution to log evaluation. This influence is pronounced in a hydrothermal reservoir where complex mineralogies occur.An appreciation of the effects of wellbore cooling and complex mineralogies on log responses should increase confidence in the evaluation of Cerro Prieto geothermal well logs. |
